exported symbols shouldn't be public by default

[nsajko]

#50105 retroactively made all exported symbols public. I think I raised this point before in some comment, but anyway exported symbols being public by default seems like a breaking change, because previously a symbol could be exported with export without being part of a public API. The notion of "being public" didn't even exist in Julia (on a language level, as opposed to docs) before that PR. A simple solution would have been to define public symbols as only the ones marked with public, although I guess now it may be too late for that?

This issue creates some problems for the Julia implementation itself, e.g. Core.Method is exported into Main, unintentionally (?) making it public, similarly with GenericMemory: #53854 #53971

If Julia v1.11 were released as-is, user packages would be locked into supporting undocumented exported symbols until they make a breaking release.

[PallHaraldsson]

Why is something exported if not part of the "public API"?

[stevengj]

Prior to the existence of the public keyword, I think most people considered exported symbols to be part of the API of a package, covered by semantic versioning. This is consistent with the old behavior of the names(::Module) function, which listed exported names by default (and now lists public names).

See also previous discussions:

• https://discourse.julialang.org/t/guidelines-for-committing-to-v1-release/34550
• https://stackoverflow.com/questions/70718619/is-there-an-api-for-julia-packages
• https://discourse.julialang.org/t/coverage-of-semantic-versioning-for-package-apis/28808
• RFC: marking private and public APIs #48819

If something is exported unintentionally, is undocumented, and sees little to no use in the Julia ecosystem, there is an argument that removing the unintended export would be a minor change allowable in a 1.x release, but this would have to be argued on a case-by-case basis.

[KristofferC]

I think it has been more or less agreed upon that exported symbols have been public. Perhaps Base has exported too much but that doesn't really change anything.